Pinned blade sealing means



July 3, 1962 H. w. WELSH 3,042,369

PINNED BLADE SEALING MEANS Filed Feb. 11, 1959 INVENTOR.

ATTORNEY United States Patent 3,042,369 PINNED BLADE SEALING MEANSHarvey W. Welsh, Indianapolis, Ind., assignor to General MotorsCorporation, Detroit, Mich., a corporation of Delaware Filed Feb. 11,1959, Ser. No. 792,664 3 Claims. (Cl. 253-77) This invention relates toa gas seal and vibration damping means.

More particularly, this invention relates to a gas seal and vibrationdamping means for use in combination with a rotor and blade assemblywherein each of the blades is secured to the rotor by a pin, and anannular seal member is mounted between the rotor and blades on the pinsto control the circulation of gas from the downstream to the upstreamside of the assembly.

Therefore, it is an object of this invention to provide a gas seal andvibration damping means in combination with a pinned rotor bladeassembly to control the circulation of gas from one portion of theassembly to another, and to dampen the blade vibration.

Other features, advantages and objects will become apparent by referenceto the detailed description of the invention and to the drawings whereinthere is shown the preferred embodiments of this invention.

In the drawings:

FIGURE 1 is a front elevational view with parts broken away andsectioned of a portion of a rotor assembly embodying this invention,

FIGURE 2 is a cross-sectional view of the rotor assembly of FIGURE 1 ona plane indicated by the lines 2-2 of FIGURE 1, and

FIGURE 3 is a front elevational view of a detail of FIGURE 1.

Referring now to the drawings and more particularly to FIGURE 1, thereis shown therein a portion of a rotor assembly of an axial flow typecompressor, the rotor assembly including a rotor or disk 12 having aplurality of circumferentially spaced blades 14 secured thereto. Each ofthe blades includes a platform 18 integral therewith, the platformhaving two tangs 20 depending therefrom to define a blade stalk, theaxial distance between the tangs being slightly greater than thethickness of the rim portion 22 of the rotor 12 with which they areadaped to cooperate. As seen in FIGURE 2, the tangs 29 have holes 24axially aligned with each other and adapted to be aligned with holes 26in the rim 22 of the rotor for the insertion therethrough of pins 28 tosecure the blades to the rotor upon straddling of the rotor rim 22 bythe tangs 20. Axial displacement of the pins is prevented by theabutment of head 29 and nuts or other retainers 30' against the tangs.

As shown more specifically in FIGURE 1, the blade platforms 18 haveedges 40 extending circumferentially beyond the tangs 20 into closeproximity to each other upon assembly to the rotor, a nominalcircumferential clearance being provided therebetween. Each of thegrooves 42 between the blade tangs extends radially outward a distancesufficient to provide a small clearance 44 between the periphery of therotor rim 22 and the base 43 of the groove together with the clearancebetween adjacent platforms permitting a slight relative rotation betweenthe blade and rotor on the pin 28 under the influences of the gasbending and centrifugal forces acting on the blades. Slight axialclearances or spaces 45 are also provided between the rotor rim 22 andthe blade tangs.

Since a pressure rise is effected from the upstream edge 46 as seen inFIGURE 2 to the downstream edge 47 of the compressor, and since thesubstantially abutting blade platforms do not constitute a seal, anyopenings or clearances large enough to bleed air therethrough, such asthe opening 48 between adjacent blade tangs and platforms and rotor rim,as well as clearances 44 and 45, will permit a reverse circulation ofthe gas or air from its normal path because of the differential inpressures of the air on opposite sides of the platforms. This reversecirculation of air causes a loss of compression resulting in lowercompressor efliciency. Accordingly, a gas seal constituting the subjectof this invention is inserted between the rotor rim and blade tangs areshown in FIGURE 2. The seal comprises a thin (.005.010" thick, forexample) annular sheet metal plate 32 having a continuous inner rim 34,an outer stepped rim 36, and a plurality of circumferentially spacedholes 38 aligned with the holes 24 and 26 in the tangs and rotor rim.The outer rim 36 has radially projecting circumferentially spacedportions 50 of a circumferential length equal to the distance betweenblade tangs of adjacent blades, i.e., equal to the length of thecombined overhang of adjacent blade platforms. The space betweenprojections 50 therefore provides recesses 52 of a circumferentiallength equal to the circumferential length of the stalk portions of eachblade assembly. The seal 32 is inserted between the rotor rim 22 and thedownstream tang 20 extending radially into close adjacency with thebottom of groove 42 as seen best in FIGURE 2 and the underside of theblade platforms 18 as seen best in FIGURE 1, effectively preventing thereverse flow of air from the downstream to the upstream portions of theblade assembly. A nominal radial clearance is provided between thebottom of the groove and the underside of the platforms with respect tothe periphery of the seal to permit a slight relative roation betweenthe parts, this clearance being sufficient to prevent an interferencefit while, however, maintaining a good seal.

In addition to controlling the circulation of air, plate 32 alsoconstitutes a vibration damping means. In a pinned blade connection ofthis kind, it frequently occurs that the blades are tuned to an excitingengine order of vibration, which can result in damage to the engine atcertain predetermined speeds. The seal 32, however, in the positionindicated, constitutes a dry friction damper to dampen these undesirablevibrational frequencies and therefore permit operation of the engine atspeeds otherwise unobtainable, i.e., the range of objectionablevibrations is raised therefore raising the permissible safe enginespeed. Since the reaction loads on the assembly tends to push theassembly upstream, the seal is inserted between the downstream tangs andthe rim so that the tangs and seal are pressed against the rimpermitting the seal to effectively dampen the objectionable vibrations.The seal therefore acts as a bearing surface upon relative movement ofthe tangs with respect to the rim, i.e., the upstream faces of the tangsand the downstream face of the rim rub against the opposite faces of theseal as they pivot about each other due: to the cenrifugal and gasbending forces acting on the blades. The tendency of the assembly to bemoved upstream because of the reaction loads also maintains theclearance between the upstream tangs and the rim for the relativerotation between the rim and tangs.

While the invention is believed to be clear from an inspection of thedrawings, a brief description of the assembly thereof is as follows. Theseal 32 is abutted against the rotor rim 22 with the holes 26 and 38axially aligned. Each of the blades with its depending tangs 20 is thenslipped over the seal and rim with the stalks fitting in the slots orrecesses 52 and the underside of the platform edges 40 cooperating withthe projections 50. Pins 28 are then inserted through the axiallyaligned holes and secured against axial displacement. The assembly isthen complete, and the seal effectively prevents reverse circulation ofair from the downstream to the upstream side and dampens the vibrationsimposed on the blade assemblies.

While the invention has been described in its preferred form for use inan axial flow type compressor, it will be clear to those skilled in theart that many modifications can be made thereto without departing fromthe scope of the invention.

I claim:

1. A rotor assembly comprising a rotor, a plurality of blades pivotallysecured to and circumferentially spaced around the outer rim of saidrotor, said blades each having a tang depending from a platform, pinmeans pivotally mounting each of said blade tangs in overlappingrelationship to the rim of said rotor, each of said platforms extendingcircumferentially beyond said tangs and substantially abutting adjacentplatforms, the construction and arrangement of said platforms and tangsdefining openings between the rotor rim and adjacent tangs and theundersides of said platforms through which fluid may pass, and acombined vibration damping and fluid seal member mounted on all said pinmeans against said rotor and tangs between said tangs and rotor andextending radially into substantially abutting relationship to saidplatforms covering said openings, said member damping blade vibrationsand blocking the flow of fluid through said openings.

2. A rotor assembly comprising a rotor, a plurality of blades pivotallysecured to and circumferentially spaced around the outer rim of saidrotor, said blades each having a stalk depending from a platform and ablade tang depending from said stalk, pin means pivotally mounting eachof said blade tangs in overlapping relationship to the rim of saidrotor, each of said platforms extending circumferentially beyond saidstalks and tangs and substantially abutting adjacent platforms, themounting of said blade tangs on said rotor providing openings betweensaid rotor rim and blade stalks through which fluid may pass, theconstruction and arrangement of said platforms and tangs defining otheropenings between the rotor rim and adjacent tangs and the undersides ofsaid platforms through which fluid may also pass, and a combinedvibration damping and fluid seal member mounted on all said pin meansagainst said rotor and tangs between said tangs and rotor and extendingradially into substantially abutting relationship to said platforms andstalks to cover all said openings, said member damping blade vibrationsand blocking the flow of fluid through said openings.

3. A rotor assembly as in claim 2, wherein said member comprises a flatdisc having a circumferentially slotted outer rim providing spacedradial projections of a circumferential length and radial extentsuflicient to cover said other openings, the portions of said discbetween said projections blocking said first-mentioned openings.

References Cited in the file of this patent FOREIGN PATENTS 202,528Australia July 13, 1956 701,263 Great Britain Dec. 23, 1953 724,281Great Britain Feb. 16, 1955 745,073 Great Britain Feb. 22, 1956 777,612Great Britain June 26, 1957 1,097,487 France Feb. 16, 1955 1,136,390France Dec. 29, 1956

